Impact and Interaction of Nitrogen and Phytophthora infestans as Yield-limiting and Yield-reducing Factors in Organic Potato (Solanum tuberosum L.) Crops

Abstract

For organic potato producers, the two main challenges are disease and nutrient management. Both are limited by regulations that on the one hand prohibit the use of chemical fertilizers, especially nitrogen, and on the other hand prohibit most synthetic pesticides. Late blight caused by Phytophthora infestans is commonly thought to be the most yield-reducing factor. However, because there is no really effective fungicide available to control late blight, there are virtually no yield loss data available for organic farming conditions. In this paper, the state of the art of organic potato tuber growth under on-farm conditions with respect to disease and nutrient management is summarized by field trials and on-farm surveys on commercial organic crops carried out in the years 1995-1998. Soil nitrogen (N) levels, plant N uptake, disease development of P. infestans and potato yield were measured. Results indicated that N availability was most important in limiting yields in organic potato crops. From on-farm data, a model including disease development, growth duration of the crops until foliage decay and different parameters related to N status of the crop could explain 73% of the observed variation in yield. Only 25% of this variation in yield could be attributed to the influence of late blight. Differences in N availability explained 48%. In conclusion, several points emerged from the results. In organic farming, yields are mainly limited by nutrient availability in spring and early summer. The effects of late blight on yields may often be overestimated and cannot be deduced from results in conventional farming because of the strong interaction with nutrient status. Depending on N availability, tubers stop growing between mid-July (70-90 kg N ha −1 uptake), the end of July (110-140 kg N ha −1 uptake) and mid-August (140-180 kg N ha −1 uptake) due to N limitations. The higher the N status of a potato crop, the longer the growing period needed to achieve the attainable yield and the higher the probability that late blight stops further tuber growth and becomes the key tuber-yield-limiting factor. In the second part of this paper, the interactive effects of soil N availability and the impact of P. infestans on yield in the presence and absence of fungicides from 1996 to 1998 for mid-early main crops are reported. An empirical schematic model of disease impact depending on N availability was developed.

Closing the Global Energy and Nutrient Cycles through Application of Biogas Residue to Agricultural Land – Potential Benefits and Drawback

“…In general, biogas residue presents an efficient nitrogen source for plants with the potential to improve crop yield and soil properties [80][81][82][83]. However, it is important to remember that N is the most common limiting factor for crop growth in organic farming systems [84][85][86][87] owing to failure in synchronizing crop N demand and supply to the soil by mineralization of organic fertilizers [88].…”

Environmental impacts of organic agriculture in temperate regions.

“…In Sweden, Kirchmann et al [53], following an 18-year trial, found the organic management system was less efficient with respect to NUE as N leaching was not reduced and weed competition reduced crop N uptake. In contrast, in Germany, both Finckh et al [116] and Möller et al [117] found that NUE can be improved under low input or organic potato production systems, possibly linked to improved crop light use efficiency when N is limiting. Halberg [110] and Halberg et al [118] found significantly higher NUE in organic versus conventional dairy farms and lower N surplus per hectare.…”

Diversität, Pflanzenernährung und Prognose: Ein integriertes Konzept zum Management der Kraut-und Knollenfäule in der Ökologischen Landwirtschaft

“…So werden unter ökologischen Bedingungen während der Hauptwachstumsphase des Blattapparates bis zum Beginn der Knollenbildung 110-130 kg N ha -1 benötigt, um ein Ertragspotenzial von 35 t ha -1 zu erreichen (Schulte-Geldermann 2008). Insgesamt werden im ökolo-gischen Anbau pro 10 t Ertrag zwischen 27 und 35 kg N benötigt (Möller et al 2006). Im Gegensatz dazu wird in konventionellen Anbausystemen von 40-50 kg N pro 10 t Ertrag ausgegangen (Harris 1992;van der Zaag 1992;Marschner 1995).…”